1. Field
Embodiments of the invention relate to engine start control systems and more particularly to an engine start control system which reverse-rotationally drives a crankshaft to a predetermined position immediately after an engine has been stopped.
2. Description of the Related Art
An idle stop (idling stop) control is known in which at the time of temporary stop, such as waiting at stoplights, and upon establishment of predetermined conditions, an engine is temporarily stopped and thereafter is restarted in response to a throttle operation to restart moving. At the time of temporarily stopping the engine by this idle stop control, “rewinding control” may be exercised in which a crankshaft is reverse-rotationally driven to a predetermined position immediately after the engine stop in order to improve engine startability. However, an appropriate position to stop the reverse-rotational drive using this idle stop control is immediately rearward of compression top dead center. Therefore, because of “swing-back,” it is difficult to stop the crankshaft at the appropriate position only by cutting electricity to an alternating-current generator starter motor along with detection of the predetermined position. During “swing-back,” a piston is pushed back by a compression reactive force to drive the crankshaft in a normal-rotational direction.
Japanese Patent No. 3,969,641 (“JP 3969641”) discloses the following technology. In “rewinding control” at the time of stopping an engine by idle stop control, when it is detected that a crankshaft is rewound to a predetermined position immediately rearward of compression top dead center, reverse-rotational drive is executed at a second duty ratio set to a value smaller than that of a first duty ratio applied to the “rewinding control.” This reduces an amount of displacement in the normal-rotational direction due to “swing-back.”
In the engine start control system, as described in JP 3969641, it is necessary to reduce the second duty ratio applied to the reverse-rotational drive to reduce the “swing-back” so not to pass compression top dead center. In some situations, the period of time from the convergence of “the swing-back” to the complete stop of the crankshaft tends to elongate. If the first duty ratio applied to the “rewinding control” is increased to increase the speed of reverse-rotational drive, “the swing-back” resulting from the compression reactive force is increased. Consequently, it is difficult to shorten the time taken to complete the “rewinding control.”